It is generally recognized that success in the marketplace, particularly with respect to fluid-absorbing articles such as disposable diapers, incontinence garments or pads and the like, depends substantially on functional efficiency, including comfort of the wearer, appearance, and price of the product being sold.
In general, such product must have a fluid-retaining core component, usually compressing one or more layers of absorbent material such as wood pulp, rayon, gauze, tissue or the like, and, in some cases, synthetic hydrophilic material such as a superabsorbent powder.
To protect clothing, and surrounding areas from being stained or wetted by fluids retained in a pad or core, such article is generally backed by a fluid-impervious backing component.
The article or fluid-absorbent pad generally also has a nonwoven-type fabric or coverstock material, which defines at least the body-contacting surface of the article. Functionally speaking, the nonwoven coverstock material is intended to help control fluid flow and insulate the wearer from continuous contact with moisture already retained in the absorbent pad or core. Such facing or coverstock must be pervious to fluids on its body-contacting side so as to promote the direct and immediate transfer of each fluid application or insult (i.e. acquisition rate) to the fluid absorbent core component; the coverstock itself, however, should be essentially nonabsorbent to fluid and remain soft and dry. It is particularly important, in this regard, to minimize potential rewet or back migration of fluid from the fluid-absorbent core component, after repeated insults, and for the cover-stock to continue to feel dry and soft without serious strength loss.
It is now generally accepted that major improvements can be achieved regarding the comfort of the wearer of such articles (a) by further increasing coverstock thickness or caliper to retain a defined physical separation between a wearer's skin and the fluid-retaining core and/or (b) by improving the above-noted fluid flow control, especially flow through and back flow or rewet properties.
With respect to such properties it is noted that continued efforts are being made for the purpose of improving flow control without adversely affecting production efficiency, strength or comfort to develop products offering such advantages.
In U.S. Pat. No. 4,798,603 of Meyer et al (assigned Kimberly-Clark) absorbent articles such as diapers, incontinence garments, wound dressings and the like are proposed, in which rewet or back fluid flow from the core or absorbent component is reduced by using a liquid permeable top sheet of synthetic hydrophobic polymer filaments having an effective average pore size larger than the absorbent core, with a liquid-permeable transport layer interposed between the top sheet and the absorbent core. The transport layer, as described, is less hydrophilic than the core, has a uniform density, and an average pore size which is less than that of the bonded top sheet layer, but greater than that of the core.
U.S. Pat. No. 4,883,790 of Newkirk (assigned to James River Corporation) utilizes a high loft nonwoven coverstock having a carded fiber web of 3 dpf or greater, bonded to a carded fiber web having an average denier of 3 or less. Each layer or web, as described, contains sufficient thermoplastic bicomponent fiber to permit inter-and intra-air bonding of the layers.
U.S. Pat. No. 4,652,484 (assigned Kao Corporation) relates to nonwoven fabrics for disposable absorbent articles such as sanitary napkins, paper diapers and the like. The articles are made of hot-melt fiber having a 90.degree.-140.degree. C. melting range and consisting of 2 layers of sterically buckled fiber having 1-3 dpf and 1.5-6 dpf respectively.
While the art, as above described, appears to recognize and attempts to address fluid flow problems plus other known deficiencies, the art has not, thus far, been able to provide a unitary nonwoven cover sheet with an efficient fluid flow control mechanism while supplying cost and other market needs including a reduced number of conventional bonding steps.